Sex ratios and sexual selection in socially monogamous zebra finches |
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Authors: | Burley Nancy Tyler; Calkins Jennifer Devlin |
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Institution: | Department of Ecology and Evolutionary Biology, University of
California, Irvine, CA 92697-2525, USA |
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Abstract: | An experiment was performed in which adult sex ratios of zebrafinches,
Taeniopygyia guttata castanotis, were varied to testpossible effects
of adult population sex ratios on sexual selectionintensity and mating system
dynamics in species with biparentalcare. The possibility that sex ratio
influences the successof social mating patterns (leading to polygyny when
males arerare and polyandry when females are rare) was not supported.Results
did support the prediction of the differential allocationhypothesis that
individuals of the abundant sex would increasetheir relative parental
expenditure (PE). Although total (male+ female) PE did not vary between
treatments, relative malePE was significantly higher in the male-biased
treatment (MBT;sex ratio 64% male) than in the female-biased treatment (FBT;
sexratio 36% male). In both treatments, male PE contributions contributedto
female reproductive rate. Results also supported the predictionof the
differential access hypothesis that individuals of theabundant sex would
experience greater intensity of selectionon sexually selected attributes.
Male beak color, a sexuallyselected trait, influenced male social parentage
in the MBTbut not in the FBT. Finally, broods in the FBT displayed higher
hatchingasynchrony and lower hatching success; we believe this was causedby
early onset of incubation, a tactic used as a defense againstintraspecific
brood parasitism, which was much higher in theFBT. Population sex ratios may
be an important factor affectingfemale ability to influence male parental
investment patterns. |
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Keywords: | differential access differential allocation parental investment sex ratio sexual selection social monogamy zebra finches |
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